Screening and identification of antibacterial agents produced by <i>Aspergillus</i> species from the soil of Bayero University Kano

Abstract

This study was conducted to isolate antibiotic producing fungi in soil samples collected from Bayero University, Kano. Soil samples were suspended in deionised distilled water and inoculated on potato dextrose agar (PDA) by spread-plate method for the isolation of fungi. Primary screening of antibiotic producers was conducted using agar well diffusion method. All the isolates were identified to be in the genus Aspergillus. Out of the sixty (60) fungal isolates, three (3) species (A. flavus, A. fumigatus and A. niger) were selected for fermentation process and extraction of metabolites using ethyl acetate. The extracts were dried and subjected to disc diffusion assay against Streptococcus pneumoniae, Staphylococcus aureus, E. coli and Pseudomonas aeruginosa. The extracts showed inhibitory activity against all the test organisms at concentration of 1000μg and 800μg with little or no activity at 600μg against the tests organisms. Highest activity was observed from the metabolites of A. fumigatus on all the test organisms with MIC values of 250μg/ml. Thin layer chromatography of all the three extracts revealed four sports per chromatogram. The chromatogram study reveals many bioactive compounds such as Oleic acid, n-Hexadecanoic acid known to have antibacterial activity against range of bacteria. Similarly, the extracts showed some level of toxicity to brine shrimp. The extracts were found to have some pharmaceutical applications and therefore should be subjected for further bioassay such as anticancer and antioxidant.

Keywords: Antibiotic producing fungi, Soil, Aspergillus, Oleic acid